1. Field of the Invention
The present invention relates to a projection optical system in which a lens and a reflection mirror are arranged, and a projection display apparatus using the same.
2. Description of the Related Art
Projection display apparatuses (also called as projectors) for projecting an image displayed on a light valve have been spreading widely in recent years.
Projection optical systems used in such projectors are generally required to have a long back focus and the entrance pupil viewed from the reduction side (light valve side) needs to be sufficiently in the distance, i.e., the reduction side is required to have telecentricity.
Further, with the recent performance improvement of light valves, good aberration correction appropriate for the resolution of the light valve is demanded for the projection optical system. Further, brighter and wider angle projection optical systems are strongly demanded in consideration of the use in bright and narrow indoor spaces for presentations and the like.
Further, projection optical systems that combine a first optical system which is a dioptric system composed of a plurality of lenses and a second optical system which is a catoptric system composed of a convex mirror are also known as described, for example, in Japanese Unexamined Patent Publication No. 2008-096761 (Patent Document 1), Japanese Unexamined Patent Publication No. 2007-017707 (Patent Document 2), and Japanese Unexamined Patent Publication No. 2009-271372 (Patent Document 3).
For a projection optical system composed only of an ordinary dioptric system, if an attempt is made to broaden the angle of view by reducing the focal length, the lens size on the magnification side inevitably becomes excessively large. In the mean time, a projection optical system composed of a dioptric system and a catoptric system can be made relatively small in comparison with a projection optical system composed only of a dioptric system and is, therefore, suitable for broadening the angle of view by reducing the focal length (Patent Documents 1 to 3).